Federal authorities investigating the deadly anthrax attacks sent divers through the ice of a secluded forest pond Monday near the former home of a scientist described by authorities as "a person of interest" in the case.
FBI spokeswoman Debra Weierman in Washington said the search was "just a continuation of our investigation on the anthrax case." She declined to provide more information.
The operation marked the second time in seven weeks that investigators have probed ponds in the Catoctin Mountains, about 45 miles west of Baltimore, for evidence of the deadly anthrax attacks.
Authorities set up at least three roadblocks around two square miles of snow-covered woodland owned by the city of Frederick, the town where former Army biological weapons researcher Dr. Steven Hatfill used to live. Hatfill has denied involvement in the October 2001 attacks.
As in December, authorities erected tents and sent divers through holes in the ice. Agents in heavy parkas watched video monitors set up on the frigid surface.
Douglas F. Nichols, a home-improvement contractor who lives near one of the roadblocks, said the road was closed Sunday. Large numbers of agents arrived Monday morning in more than a dozen vehicles, he said.
"There's been an incredible amount of activity going on up and down the road," Nichols said.
The site is about two miles south of another group of ponds federal agents combed in December during a weeklong search for evidence related to the anthrax letters that killed five people and infected 18 others.
The area closed off Monday was about two miles long and a mile wide, in the hills above Fishing Creek Reservoir, a source of city drinking water. The area, located about four miles northwest of the city, contains eight ponds.
Local resident Gregory Maddox said FBI officials told him a roadblock near his home would be up for about a week.
"I kind of support what they're doing," Maddox said. "I believe whatever it is they're doing benefits the entire United States, therefore, I don't ask them a lot of dumb questions."
Orange barrels and signs marked off sections of Hamburg and Fishing Creek roads, winding mountain lanes that follow rushing streams and pass scattered homes. Officials sat in vehicles at each closure. A woman at one roadblock identified herself as an FBI agent, but referred all questions to the agency's public relations office.
The FBI issued a statement last week, prompted by questions about flight restrictions over the search areas, confirming that the operation was part of the anthrax investigation.